Hepatitis B virus (HBV) encoded x antigen (HBxAg) is a trans-activating protein that contributes to the development of hepatocellular carcinoma (HCC) by altering expression of selected hepatocellular genes. To identify some of these genes, HBxAg or vector were introduced into the human hepatoblastoma cell line, HepG2, and differentially expressed genes were identified by PCR select cDNA subtraction. Differential expression of these genes was verified by in situ hybridization (ISH) and immunohistochemistry (IHC) of HBV infected compared to uninfected liver samples. Costaining of HBxAg with several up-regulated proteins implies that each may be up-regulated by HBxAg or be a cellular response to HBxAg in vivo. To determine whether these up-regulated gene (URG) products or corresponding antibodies to them exist in serum, appropriate ELISAs were designed. In retrospective longitudinal studies, antibodies to multiple URGs were detected in the sera from 23 of 25 (>90%) of Korean carriers with HCC an average of 3 years prior to tumor diagnosis, in 18 of 24 (75%) of Korean carriers with dysplastic and/or regenerative nodules but no HCC, and in <15% of asymptomatic carriers. Additional cross-sectional and longitudinal prospective studies in other carrier populations are required to validate these markers. Hence, the objective of this proposal will be to establish the clinical utility of these antibodies in various HBV carrier populations at risk for the development of HCC. Given that Chinese and African patients come from regions of the world with the highest incidence of HBV infection and HCC, cross-sectional (aim 1) and longitudinal (aim 2) studies will be conducted to determine whether these markers are prevalent in tumor bearing patients and/or in those at high risk for tumor development, respectively. Additional work will determine the specificity of these markers using serum samples from patients who are not HBV infected (aim 3). Antibodies to other HBxAg URGs will also be tested to optimize the sensitivity, specificity and predictive value;of the antibody panel (aim 4). This work will establish a rapid, simple, inexpensive and noninvasive blood test for early HCC that will save many lives by permiting early detection and curative intervention.